Facultad de Ingeniería y Ciencias Aplicadas

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33
(33, 33) Saleh-Cumsille, Javier; Cruz, Pedro; Huiliñir, Cesar; Scott, Felipe; Vergara-Fernández, Alberto; 33
BACKGROUND: This article proposes a new methodology for calculating k_La in airlift reactors (ALRs) based on a digital imaging technique and Higbie's model. Four ARLs with different internal diameters (28, 37.4, 45, and 55 mm) were used to determine the aeration patterns, velocities, and size distributions of the bubbles. Video recordings lasting 10 s were recorded using a 1080p slow-motion camera at 240 frames per second (fps). In 100 frames per video, between 500 and 599 frames, the characteristics of the bubbles were captured and then processed using the sci-kit-image Python package. RESULTS: The Higbie model coupled with image analysis was used to determine k_L, and was then compared with the experimental values and k_La correlations. As a result, bubble velocities between 0.2 and 0.8 m s^?1 were determined. CONCLUSIONS: The k_La values (20–28 h^?1) calculated using the new methodology were close to the experimental values and were compared with the correlations for ALRs.
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(33, 33) Pavez, Lukas; Saavedra, Jose M.; 33
During the last years, we have seen significant advances in the object detection task, mainly due to the outperforming results of convolutional neural networks. In this vein, anchor-based models have achieved the best results. However, these models require prior information about the aspect and scales of target objects, needing more hyperparameters to fit. In addition, using anchors to fit bounding boxes seems far from how our visual system does the same visual task. Instead, our visual system uses the interactions of different scene parts to semantically identify objects, called perceptual grouping. An object detection methodology closer to the natural model is anchor-free detection, where models like FCOS or Centernet have shown competitive results, but these have not yet exploited the concept of perceptual grouping. Therefore, to increase the effectiveness of anchor-free models keeping the inference time low, we propose to add non-local attention (NL modules) modules to boost the feature map of the underlying backbone. NL modules implement the perceptual grouping mechanism, allowing receptive fields to cooperate in visual representation learning. We show that non-local modules combined with an FCOS head (NL-FCOS) are practical and efficient. Thus, we establish state-of-the-art performance in clothing detection and handwritten amount recognition problems.
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(33, 33) Tapiero, Yesid; Aravena, Yajaira; Vargas, Gustavo; Sánchez, Julio; Huiliñir, Cesar; 33
Swine wastewater is recognized as a significant environmental concern due to its high concentrations of ammonium nitrogen (N-NH₄⁺), which typically range from 400 to 4500 mg L^?1. To address this issue, the application of polymer-enhanced ultrafiltration (PEUF) has been proposed as a method for removing N-NH₄⁺ from aqueous media. This study utilized sodium poly(acrylate) (PNaA) and potassium poly(3-sulphopropyl acrylate) (PKSPA) as adsorbents for NH₄⁺ removal. Key operating parameters, including pH, polymer dosage, initial NH₄⁺ concentration, and applied pressure, were analyzed. With PNaA, the presence of divalent cations did not negatively affect the retention performance, which remained at 72 %, nor did it impact the permeate flux. In contrast, when PKSPA was used, the strong competition between NH₄⁺, Ca²⁺, and Mg²⁺ ions for the functional groups resulted in a decrease in NH₄⁺ retention, dropping from 71 % to 59 %, along with a lower permeate flux. The enrichment method identified a maximum N-NH₄⁺ removal capacity of 685.7 mg N g^?1 PKSPA when treating simulated wastewater from the swine industry. The observed decrease in permeate flux was attributed to the formation of macromolecular aggregates, which blocked the pores of the ultrafiltration membrane. Thus, PEUF emerges as a promising approach for the removal of N-NH₄⁺ from swine wastewater.
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(33, 33) Aldea, Sofía; Bazáez, Ramiro; Heresi, Pablo; Astroza, Rodrigo; 33
Bridges are one of the most critical and costly structures on road networks. Thus, their integrity and operation must be preserved to prevent safety concerns and connectivity losses after seismic events. Recent large-magnitude earthquakes have revealed a series of vulnerabilities in multi-span highway bridges. In particular, skewed bridges have been severely damaged due to their susceptibility to developing excessive in-plane deck rotations and span unseating. Although seismic design codes have been updated to prescribe larger seating lengths and have incorporated unseating prevention devices, such as shear keys and cable restrainers, research on the seismic performance of skewed bridges with passive energy-dissipation devices is still limited. Therefore, this study focuses on assessing the effectiveness of implementing hysteretic dampers on skewed bridges. With that aim, dampers with and without recentering capabilities are designed and incorporated in representative Chilean skewed bridges to assess their contribution to seismic performance. Three-dimensional nonlinear finite element models, multiple-stripe analysis, and fragility curves are utilized to achieve this objective. The results show that incorporating bidirectional dampers can effectively improve the seismic performance of skewed bridges at different hazard levels by limiting in-plane deck rotations independently of their skew angle. Additionally, the influence of external shear keys and damper hysteretic behavior is analyzed, showing that these parameters have a low influence on bridge performance when bidirectional dampers are incorporated.
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(33, 33) Baier, Carlos R.; Melin, Pedro E.; Torres, Miguel A.; Ramirez, Roberto O.; Muñoz, Carlos; Quinteros, Agustin; 33
Grid-connected power inverters are indispensable in modern electrical systems, playing a pivotal role in enhancing the integration of renewable energies into power grids. Their significance, primarily when functioning as grid-forming inverters, extends to maintaining the grid’s inertia and strength—a distinct advancement over traditional grid-following operations. As grid-forming inverters, these devices emulate the characteristics of synchronous generators and can act as robust voltage sources, providing essential ancillary services. This behavior is particularly relevant when integrating energy storage systems on the converters’ direct current side. Among the various inverter topologies, the current source inverter (CSI) has emerged as a promising yet underexplored alternative for grid-forming applications. CSIs, when paired with their AC output filters, can effectively operate as voltage sources, utilizing control strategies that facilitate the integration of renewable energies into the electrical system. Their design inherently manages output current fluctuations, reducing the need for restrictive current limitations or additional protective measures. This paper examines the operational region of CSIs, obtained through detailed modeling, to explore their advantages, challenges, and potential for enhancing grid-connected systems. Analyzing the operating region from the converter model verifies the limits of where the converter can operate in a plane of active and reactive powers. For a small prototype model operating with 7 amperes in DC and 120 V in AC, it is possible to supply or absorb active power exceeding 1000 W and manage maximum reactive power values around 500 VAr, as determined by its operating region. Simulations also confirm that small changes in the control reference, as little as 5%, towards the region’s right limits cause significant oscillations in the dynamic control responses. This research aims to deepen our understanding of CSIs’ operational capabilities and highlight their unique benefits in advancing grid-connected systems and promoting the integration of renewable energy using this technology.
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(33, 33) Moreno-Palacio, Diana P.; Gonzalez-Calderon, Carlos A.; Posada-Henao, John Jairo; Lopez-Ospina, Hector; Gil-Marin, Jhan Kevin; 33
This paper presents an entropy-based transit tour synthesis (TTS) using fuzzy logic (FL) based on entropy maximization (EM). The objective is to obtain the most probable transit (bus) tour flow distribution in the network based on traffic counts. These models consider fixed parameters and constraints. The costs, traffic counts, and demand for buses vary depending on different aspects (e.g., congestion), which are not captured in detail in the models. Then, as the FL can be included in modeling that variability, it allows obtaining solutions where some or all the constraints do not entirely satisfy their expected value, but are close to it, due to the flexibility this method provides to the model. This optimization problem was transformed into a bi-objective problem when the optimization variables were the membership and entropy. The performance of the proposed formulation was assessed in the Sioux Falls Network. We created an indicator (?) that measures the distance between the model’s obtained solution and the requested value or target value. It was calculated for both production and volume constraints. The indicator allowed us to observe that the flexible problem (FL Mode) had smaller ? values than the ones obtained in the No FL models. These results prove that the inclusion of the FL and EM approaches to estimate bus tour flow, applying the synthesis method (traffic counts), improves the quality of the tour estimation.
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(33, 33) Sánchez, Luis; Aguila, Gonzalo; Araya, Paulo; Quijada, Sergio; Guerrero, Sichem; 33
The transient combustion of biomass leads to the evolution of a variety of pollutants (NO, CO, organic compounds, and many others) that can react with each other on a suitable catalyst to generate compounds of lower toxicity. Here, the transient reduction of NO with CO and naphthalene in the presence of oxygen was studied on a Ca/Cu/YCeO₂-TiO₂catalyst. Response surface methodology was used to identify the optimum amounts of calcium, copper, and cerium. The optimized Ca/Cu/YCeO₂-TiO₂catalyst was then extensively studied and characterized. The coupling of yttrium-stabilized ceria with TiO₂provided an active support that effectively activated naphthalene. When calcium and copper were added to the support, the obtained Ca/Cu/YCeO₂-TiO₂catalyst achieved the full conversion of CO and naphthalene and 72% conversion of NO. The Ca/Cu/YCeO₂-TiO₂catalyst possessed labile oxygen species, which might be related to the high catalytic activity.
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(33, 33) Paul, Alvaro; Rashidi, Mehdi; Kim, Jin Yeon; Jacobs, Laurence J.; Kurtis, Kimberly E.; 33
With the increase of aggregate quarrying to meet the growing need for concrete construction comes a risk associated with new aggregate sources, which may not have uniform compositions and contain potentially harmful substances, such as sulfate and sulfide. To provide insights into the impact of sulfate- and sulfide-bearing sand on susceptibility to delayed ettringite formation (DEF), this study measures the evolution of expansion, acoustic nonlinearity (representing microscale damage), and dynamic elastic modulus of mortars prepared with varying cement compositions and exposed to an early-age high-temperature curing cycle. Samples containing sulfate- and sulfide-bearing sand show substantially higher initial levels of damage, with expansion starting at earlier ages than control samples. Damage in mortars using this sand can be attributed to accelerated decomposition of alkali-feldspar, microcracking due to relative thermal deformation between phases, early release of alkali that increases the amount of sulfate in the pore solution, and release of sulfate ions from aggregates.
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(33, 33) Fernández, Rodrigo; Depiano, Rafael; 33
The literature on the relationships between delays and queue lengths as a function of the degree of saturation at road junctions is plentiful. However, little has been written about similar relationships at bus stops. In this article we show delay and queue length functions in bus stops to study their properties by using an ad-hoc simulation model. It was found that delay and queue functions at bus stops differ from that observed at road junctions. The main characteristic is that the functions increase more smoothly at bus stops than at road junctions. Therefore, in the process of designing and operating bus stops, not only the nominal capacity but also a low degree of saturation should be considered to manage congestion in the stop area. In addition, if the bus stop is located upstream of a traffic signal, the green time, and the cycle time play an important role in reducing congestion. This is relevant because on arterial roads most bus stops are close to traffic signals.
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(33, 33) Gómez-Padilla, Alejandra; González-Ramírez, Rosa G.; Alarcón, Fernando; Voß, Stefan; 33
We propose an option contract model for the leasing of containers. In an option contract, the shipping company commits to order a quantity of containers from the leasing company and has the right to modify its order at a later stage, according to its actual requirement. Under this scheme, the shipping company is allowed to request a smaller or larger number of containers than the agreed initial order. This is done by buying an option premium in advance from the container leasing company. We present numerical results for different scenarios based on information provided by experts in the industry. For the purposes of comparison, a nonoption contract scheme is also evaluated. According to our numerical results, an option contract is better under a scenario where demand is normally distributed with a large standard deviation. This scenario is commonly observed in practice due to the dynamism and volatility of the shipping industry. We conclude that, under an option contract scheme, the shipping company has more flexibility to adjust its demand for containers and to be requested from the leasing company, and this adjustment is compensated by an option price determined according to variations in demand.
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(Springer New York LLC, 33) Astroza, Rodrigo; Hernández, Francisco; Díaz, Pablo; Gutierrez, Gonzalo; 33
A full scale five-story reinforced concrete building was built and tested on the Large High Performance Outdoor Shake Table (LHPOST) at the University of California, San Diego in 2012. The main objective of the test program was to study the seismic response of the structure and the nonstructural components (NSCs) and their dynamic interaction at different levels of seismic excitation. The building specimen was first tested base-isolated and then fixed at its base. In the fixed-base configuration, a suite of six earthquake motions of various intensities was applied to the building to progressively increase the seismic demand. In this paper, the modal parameters of the fixed-base building are identified using the input-output dynamic data recorded during the seismic tests. The deterministic-stochastic subspace identification method (DSI) is employed to estimate the variations of the modal properties of the building during the seismic tests by employing a short-time windowing approach. The changes of the modal parameters during the seismic motions are tracked, analyzed, and compared to those previously obtained from ambient vibrations and low-amplitude white noise base excitation tests. The identified natural frequencies and equivalent damping ratios of the building changed with the intensity of the input motions and damage in the structure, while the mode shapes are found to be insensitive to them.
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(33, 33) Birrell, Matías; Li, Yong; Astroza, Rodrigo; 33
A key aspect of performance assessment of structures is the quantification and propagation of uncertainties, from the estimation of hazards to possible losses. In particular, probabilistic structural analysis deals with aleatory and epistemic sources of uncertainty in nonlinear modeling. Materials and components in structural models are represented by uncertain parameters, which can be accounted for via probabilistic constitutive models. The variability at a local level is then propagated to the system level when the structural model is sampled, sometimes inducing great uncertainty in structural demands. However, probabilistic modeling of real structures via finite element (FE) models has been a challenge due to high computational costs. One avenue to reduce this cost and make probabilistic modeling viable in practice is to develop cost-effective surrogate models. In this paper, a Gaussian Process (GP) approach is proposed to study the composition of parameter-induced uncertainty in mechanics-based nonlinear FE structural model responses. The methodology is validated by evaluating common regression error metrics between the original FE models and their GP surrogates. Case studies of two structures are presented, including a five-story reinforced concrete (RC) building and a five-span RC highway bridge. Finally, the low computational cost of the surrogate models is leveraged to perform simulation-based global sensitivity analysis using Sobol indices to quantify parameter-induced uncertainty in structural responses.
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(33, 33) Cedillo-Campos, Miguel Gastón; González-Ramírez, Rosa G.; Camacho-Vallejo, José Fernando; Villalobos, J. Rene; 33
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(33, 33) Meza, Armando; Latorre, Paolo; Bonacic, Milena; López-Ospina, Héctor; Pérez, Juan; 33
This paper presents a profit optimization model for substitute products in a competitive, time-sensitive market with scarcity and shifting user preferences. The model maximizes profit, considering production costs and inventory maintenance. It uses a discrete choice model to represent demand, sensitivity to price, availability, and changing preferences. A two-phase PSO-type metaheuristic solution tackles the nonlinear, recursive model, efficiently managing inventories and evolving consumer preferences. The model integrates production decisions, inventories, and sales prices, considering scarcity conditions and user preferences. It uses a multinomial logit for the consumers’ demand function with soft exogenous constraints, which influence utility and change consumption preferences and choices. This research offers a tool for companies to manage stock, production, and pricing in a context where goods are substitutes, providing a new perspective on business strategy.
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(33, 33) Carrasco, Samuel; Silva, Javier; Pino-Cortés, Ernesto; Gómez, Jaime; Vallejo, Fidel; Díaz-Robles, Luis; Campos, Valeria; Cubillos, Francisco; Pelz, Stefan; Paczkowski, Sebastian; Cereceda-Balic, Francisco; Vergara-Fernández, Albero; Lapuerta, Magín; Pazo, Amparo; Monedero, Esperanza; Hoekman, Kent; 33
The effect of magnesium chloride as an additive of hydrothermal carbonization (HTC) of lignocellulosic biomass (Pinus radiata sawdust) was studied. The HTC tests were carried out at fixed conditions of temperature and residence time of 220 °C and 1 h, respectively, and varying the dose of magnesium chloride in the range 0.0-1.0 g MgCl₂/g biomass. The carbonized product (hydrochar) was tested in order to determine its calorific value (HHV) while using PARR 6100 calorimeter, mass yield by gravimetry, elemental analysis using a LECO TruSpec elemental analyzer, volatile matter content, and ash content were obtained by standardized procedures using suitable ovens for it. The results show that using a dose of 0.75 g MgCl₂/g biomass results in an impact on the mass yield that was almost equal to change operating conditions from 220 to 270 °C and from 0.5 to 1 h, without additive. Likewise, the calorific value increases by 33% for this additive dose, resulting in an energy yield of 68%, thus generating a solid fuel of prominent characteristics.
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(33, 33) Palominos, Nicolás; Pagés-Díaz, Jhosané; Tello, Mario; Guerrero, Lorna; Huiliñir, Cesar; 33
The integration of sequential nitrification/mixotrophic denitrification (SNMD) in a single bioreactor is rarely reported. This study adapted an industrial inoculum to SNMD in a single bioreactor configuration, comparing a conventional sequencing batch reactor (SBR) and a zeolite-carrier SBR (SBBR) over 276 days across three phases: sequential nitrification heterotrophic denitrification (SNHD) adaptation, increased TAN loading, and SNMD with sulfide (HS^--S) addition. Under SNHD conditions, both systems achieved > 99 % TAN removal with complete NO₃^–-N reduction. After HS^--S addition, NO₂^–-N accumulated, yet denitrification recovered after 90 days. Under SNMD, TAN removal averaged 93.4 ± 5.6 % in the SBR and 90.0 ± 10.6 % in the SBBR (p > 0.05). While performance remained similar, zeolite influenced microbial community composition, particularly under sulfur-driven conditions. Therefore, the SNMD process was successfully developed in a single reactor, with or without zeolite, which only affected microbial abundance.
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(33, 33) San Martin-Davison, Jessica; Scott, Felipe; Vergara-Ojeda, Christian; Moreno-Casas, Patricio; Hort, Cecile; Vergara-Fernández, Alberto; 33
BACKGROUND: Indoor air pollution is a growing problem worldwide that causes a series of health issues in the population. Effective devices for abatement of volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) are currently restricted to adsorption systems based on active carbon. The objective of this study was to evaluate the operation of a new design of radial-flow biopurifier using a model mixture of toluene, benzo(?)pyrene (BaP) and formaldehyde, initially inoculated with the filamentous fungus Fusarium solani and the bacterium Rhodococcus erythropolis. RESULTS: The results show that, under the range of inlet load tested and under continuous operation, the biopurification system achieved removal efficiencies above 90%, translating into a purifier air refreshment capacity of 0.62, 2.5 and 0.8 h^?1 for BaP, formaldehyde and toluene, respectively. CONCLUSION: The system was operated for 8 months, without a decrease in the single-pass removal efficiency, and withstood up to 15 days starvation periods with a marginal effect on its air refreshment capacity once the feeding of pollutants was restarted.
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(33, 33) Lalla-Ruiz, Eduardo; López-Plata, Israel; Expósito-Izquierdo, Christopher; Barrios-Fleitas, Yeray; González-Ramírez, Rosa G.; 33
Container terminals are essential nodes in global trade, facilitating worldwide cargo flows between various transport modes. However, their operations contribute significantly to global emissions, producing greenhouse gases like CO₂ and pollutants such as nitrogen oxide. Mitigating that impact requires integrating green technologies and goals as well as exploiting renewable energy sources into terminal planning and decision support systems. Optimization techniques are key for driving terminals into this green transformation. In recent years, there has been a relevant increase in research and attention to greening ports. This growing interest includes the development of effective strategies and optimization approaches to reduce the terminal's environmental impact. This systematic literature review examines relevant studies in optimization and greening terminals from the past two years, highlighting examples such as implementing microgrids, cold ironing, autonomous electric vehicles, retrofitting yard machinery, or promoting truck platooning. We propose a research agenda to guide future efforts in this direction.
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(33, 33) Moreno-Palacio, Diana P.; Gonzalez-Calderon, Carlos A.; López-Ospina, Héctor; Gil-Marin, Jhan Kevin; Posada-Henao, John Jairo; 33
This paper presents an improved entropy-based freight tour synthesis (FTS) using fuzzy logic (FL). One approach used in formulating FTS models is entropy maximization, which aims to obtain the most probable freight (trucks) tour flow distribution in a network based on traffic counts. These models consider fixed parameters and constraints. However, the variations in costs, traffic counts, and truck demands depending on human behavior, are not always captured in detail in such models. FL can include such variabilities in its modeling. The flexibility FL provides to the model allows to obtain solutions where some or all the constraints do not entirely satisfy—but are close to—their expected values. Moreover, the modeling approach used based on FL theory is the membership function, specifically the triangular membership function, which is defined by three points corresponding to the vertices. This optimization problem was transformed into a bi-objective problem when the optimization variables are the membership and the entropy. The performance of the proposed formulation was assessed in the Sioux Falls network. To solve the problem, the model was run in General Algebraic Modeling System (GAMS), applying the ? approach, where ? value (?? [0, 1] with steps of 0.01) represents the level of accomplishment that at least one of the constraints (but can be more) gets. The results show that the entropy value decreased as the accomplishment level increased, and this behavior indicates a Pareto frontier, which proves that the optimization problem is bi-objective.
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(33, 33) González, Rosa Guadalupe; Villalobos, J. Rene; Meneses, Cesar; 33
Purpose: This paper explores the effect of port's service time, particularly the mean and variability, on shippers' total landed costs to determine the competitive position of the port and derive recommendations for the strategic design of port services. Design/methodology/approach: The competitive position of a port is estimated considering the service level offered to the end-users of the port such as port service time, its variability and its effect on the total landed costs observed by the port users. The proposed methodology is meant to help ports to determine the required service time levels to maintain or gain a competitive advantage against other ports, in terms of attracting common hinterland's customers. Findings: Results show the advantages of considering service levels factors to determine the competitive position of a port, and what are the minimum characteristics required to capture more traffic volumes, that can help port managers to take strategic design decisions to better position the port in the current fierce market. Research limitations/implications: The proposed methodology is illustrated by considering a case study, which is the Port of Guaymas in Mexico. Data was not directly collected by the port, but based on interviews with shippers and public information, a representative case is presented. Due to a confidentiality agreement with the Port, specific references for most of the data used to estimate the model's parameters are not provided. The analysis is intended to show the potential value of this mechanism and can be used for evaluating the competitive position, from a high-level perspective, of any port to determine potential hinterland by improving the service level of the port. Originality/value: The existing literature on port choice and port competition has not previously considered the effect of port service levels under the perspective of total landed costs of the users, being this paper a contribution to fulfill this gap.